As part of a NIH-sponsored fluorochemical synthetic program, a number of new compounds of potential value as red blood cell substitutes were made. The flurocarbons being tested here were made by one of the NIH contractors and were mainly cyclic structures containing only carbon and fluorine having vapor pressures between 2 and 20 torr. These compounds have been highly purified as judged by conventional chemical and physical criteria and by gas chromatographic, mass spectrophotometric, infrared spectrophotometric, and nuclear magnetic resonance analysis. Among these compounds are perfluoroalkylcyclohexanes, bicyclic and tricyclic ring structures, alkyl adamantanes, and adamantane derivatives. As emulsions, they will be evaulated by techniques developed here largely for the study of perfluorodecalins for intravenous toxicity, distribution within tissues of the body, transpiration rate through skin and lung, and the rate at which they leave specific organs, mainly the liver and spleen. In addition, some will be studied more extensively using larger animals including the baboon. Most of the work here involves awake, normal, inbred mice. It is expected that this research, besides possibly providing new actual components for artificial blood substitutes, will help form the theoretical foundation for future fundamental studies of the use of these substances in biology.